Transportation systems include automobiles, buses, trains, and other modes of transportation. Example transportation systems include the public transit systems of many metropolitan areas. In a transit system, the transit vehicle typically follows a set route. The route is a path from station to station or from stop to stop.
Occasionally, transit vehicles do not follow the scheduled routes. In the example of bus routes, a bus may be re-routed because of a traffic incident (e.g., an accident or congestion), a flood, an event (e.g., a parade or motorcade), or a variety of reasons. In the example of train routes, track construction, or accident may cause the train to use a different line of tracks. Sometimes the re-routing is scheduled and sometimes the re-routing occurs without warning.
Transit vehicles may also deviate from schedules because of delays arising from route deviations or re-routes. Ideally, each vehicle on the route arrives at each station or stop on the path according to a precise schedule. However, several events can disrupt the schedule. In the example of bus routes, an accident or congestion can cause traffic, which delays the buses. In addition, when many riders have congregated at a stop, the bus is delayed as riders enter the bus and scan their fare cards. In the example of train routes, heavy usage or interference by other trains causes delays for riders to board and disembark.
These usage types of delays tend to snowball. When a bus is late, more riders aggregate at a stop. When the bus arrives, more time is required to board all of the extra riders. Fewer riders are at the stop when the next bus arrives, which causes the next bus to spend less time at the spot and tend to catch up with the first bus.
Both temporal and spatial deviations of transit vehicles impair the ability of users to predict when the transit vehicle will arrive at a stop or station and/or locate the new location of the stop or station.